Collecting device for gases and aerosol, methods of making, and methods of use

ABSTRACT

Embodiments of the present disclosure provide for collection devices, methods of making collection devices, methods of collecting gases and aerosol particles, and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional applicationentitled “COLLECTING DEVICE FOR GASES AND AEROSOL, METHODS OF MAKING,AND METHODS OF USE,” having Ser. No. 61/393,978, filed on Oct. 18, 2010,which is entirely incorporated herein by reference.

STATEMENT OF GOVERNMENT SPONSORSHIP

This invention was made with Government support under Contract/Grant No.FIPR 08-05-069, awarded by the Florida Institute of Phosphate Research.The Government has certain rights in this invention.

BACKGROUND

Various sampling devices have been applied to collect particles orgases, separately. Some researchers have also made effort to sampleaerosols and gas simultaneously. To sample acidic gases and aerosols inworkplace air, NIOSH Method 7903, which uses one section of glass fiberplug for capturing aerosol followed by two sections of silica gel forcollecting gases, is approved by OSHA (Occupational Safety and HealthAdministration) and commonly used in occupational environments such asphosphate fertilizer manufacturing facilities, sulfuric acid productionfactories and other industries. However, recent studies have shownsampling artifacts when certain gases are present, e.g., SO₂ gas isadsorbed and the extraction process causes artifact sulfuric acid.Therefore, it is necessary to develop a new personal sampler to overcomethese deficiencies.

SUMMARY

Embodiments of the present disclosure provide for collection devices,methods of making collection devices, methods of collecting gases andaerosol particles, and the like.

An embodiment of the collection device, among others, includes: amembrane denuder, wherein the membrane denuder is a porous structurethat includes at least one chemical composition that collects at leastone type of gas; and a filter pack, wherein the filter pack collectsaerosol particles that pass through the membrane denuder, wherein themembrane denuder is disposed on top of the filter pack so that the airflow of the gas into the device passes through the membrane denuderbefore contacting the filter pack. In an embodiment, the collectiondevice also includes an impactor disposed on the membrane denuder on theside opposite the filter pack so that the gas passes through theimpactor before contacting the membrane denuder, and wherein theimpactor removes large aerosol particles.

An embodiment of the collection device, among others, includes: removinglarge particles from a gas flow using an impactor; collecting one ormore gas types using a membrane denuder after removing the largeparticles; and collecting one or more aerosol types using a filer packafter collecting the gas using the denuder.

Other structures, methods, features, and advantages of the presentdisclosure will be, or become, apparent to one with skill in the artupon examination of the following drawings and detailed description. Itis intended that all such additional structures, methods, features, andadvantages be included within this description, be within the scope ofthe present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosed devices and methods can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily to scale, emphasis instead being placedupon clearly illustrating the relevant principles. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1.1 illustrates a collection device including a membrane denuderdisposed on a filter pack, where the gas enters the membrane denuderfrom the top and then proceeds to the filter pack.

FIG. 1.2 illustrates another embodiment of the collection device thatincludes an impactor disposed on the membrane denuder, where themembrane denuder is disposed on the filter pack.

FIG. 1.3 illustrates a more detailed schematic of an embodiment of acollection device.

FIG. 2.1 illustrates the structure of the personal sampler.

FIG. 2.2 illustrates the structure of the impactor.

FIG. 2.3 illustrates exemplary designs of the porous membrane denuder.

FIG. 2.4 shows the cross structure of the denuder.

FIG. 2.5 shows the structure of the filter pack.

FIG. 2.6 illustrates a graph illustrating SO₂ removal efficiency of thefabric denuder as a function of time.

FIG. 2.7 illustrates a graph showing the impactor performance comparedwith respirable convention.

FIG. 2.8 illustrates the particle loss in the denuder.

FIG. 3.1 illustrates schematics of the PMD III.

FIG. 3.2 illustrates the experimental setup for testing gas collectionefficiency.

FIG. 3.3 illustrates the SO₂ removal efficiency of GHD and PMDs as afunction of time.

FIG. 3.4 illustrates PMD III's and IV's capacities for 4 ppm HNO₃ and 10ppm HCl gas.

FIG. 3.5 illustrates schematics of the PMD

FIG. 3.6 illustrates SO₂ removal efficiency of PMD V as a function oftime.

DETAILED DESCRIPTION

Before the present disclosure is described in greater detail, it is tobe understood that this disclosure is not limited to particularembodiments described, and as such may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present disclosure, the preferredmethods and materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present disclosure is not entitled to antedate suchpublication by virtue of prior disclosure. Further, the dates ofpublication provided could be different from the actual publicationdates that may need to be independently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of environmental engineering, biology, chemistry,materials science, mechanical engineering, and the like, which arewithin the skill of the art.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toperform the methods and use the probes disclosed and claimed herein.Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.), but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by volume,temperature is in ° C., and pressure is at or near atmospheric. Standardtemperature and pressure are defined as 20° C. and 1 atmosphere.

Before the embodiments of the present disclosure are described indetail, it is to be understood that, unless otherwise indicated, thepresent disclosure is not limited to particular materials, reagents,reaction materials, manufacturing processes, or the like, as such canvary. It is also to be understood that the terminology used herein isfor purposes of describing particular embodiments only, and is notintended to be limiting. It is also possible in the present disclosurethat steps can be executed in different sequences where this islogically possible.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a compound” includes a plurality of compounds. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

Discussion

In accordance with the purpose(s) of the present disclosure, as embodiedand broadly described herein, embodiments of the present disclosure, inone aspect, relate to collection devices, methods of making collectiondevices, methods of collecting gases and aerosol particles, and thelike. An embodiment of the present disclosure can be used as a personalsampler that can sample aerosol and gas simultaneously withoutinterference to each other and can be used in occupational environmentwhere pollutant concentration of the interest is high.

Embodiments of the present disclosure allow for the collection of gasesand aerosol particles while preventing either from interfering with thedetection of the other (e.g., artifacts that lead to improperdetermination of the gas(s) and/or aerosol particles present), which isa problem with many other devices and methods. In general, the gas isfirst collected and then the aerosol particles of interest arecollected, and this prevents gases interfering with the aerosolparticles collected on the filter surface. Embodiments of the presentdisclosure can be used to detect gases such as HCl gas, SO₂ gas, HF gas,HNO₃ gas, and NH₃ gas and aerosols such as H₂SO₄ and H₃PO₄, with lessthan 5% or without any artifacts.

Industrial hygienists, environmental health and safety personnel and thelike, can use embodiments of the present disclosure to characterizehazardous gases and/or aerosols in the work place or at home.Embodiments of the device are modular, small, lightweight and compact(e.g., about 37 mm in diameter and about 50 mm in length) with highcapacity (e.g., 100 mg of SO₂) so that the device can be worn on a beltor other similar strap so that use of the device is convenient andrepresents where a person actually works as opposed to a stationaryposition. Embodiments of the present disclosure can be used inindustries such as fertilizer manufacturing, acid production,electroplating, semiconductor, battery, metal smelting, machining, andthe like. Meanwhile, the portability of such a compact system alsoallows it to be deployed for ambient sampling network to cover a widearea or indoor air sampling.

FIGS. 1.1 and 1.2 illustrate two embodiments of the present disclosure.FIG. 1.1 illustrates a collection device including a membrane denuderdisposed on a filter pack, where the gas enters the membrane denuderfrom the top and then proceeds to the filter pack. FIG. 1.2 illustratesanother embodiment of the collection device that includes an impactordisposed on the membrane denuder, where the membrane denuder is disposedon the filter pack. FIG. 1.3 illustrates a more detailed schematic of anembodiment of a collection device.

In the embodiments shown in FIGS. 1.2 and 1.3, the air moves through theimpactor, through the membrane denuder, and to the filter pack. Ineither embodiment, the device can include a structure that holds the twoor three components and is modular so the membrane denuder and filterpack can be easily removed and analyzed (and replaced). The gas or airflow through the collection device can be controlled by a pump to pullthe gas through the collecting device, where the pump pulls from thearea below the filter pack.

In an embodiment, the sampling flowrate of the collection device isabout 0.5 to 5 Liter per minute. In an embodiment, the collectionefficiency of gases of interest is about 80% to 100%. In an embodiment,the collection efficiency of the aerosol particles by the impactor isabout 10% to 100%, depending on the particle size, and by the filterpack is about 90% to 100%.

The impactor, when included in the collecting device, can be used toremove large aerosol particles and/or can be used to classify differentsizes of aerosol particles. By designing different nozzle numbers andsizes in the impactor, the impactor can follow different particlecollection patterns, e.g., human respiratory pattern (respirablefraction, thoracic fraction or inhalable fraction) or air qualitystandard (PM2.5, PM10).

In an embodiment, the impactor includes one or more inlets to thecollection device and one or more exits at the bottom of the impactor onthe side adjacent the membrane denuder. In an embodiment, the entranceand the exit are not in line with one another so that large aerosolparticles do not flow directly into the membrane denuder. On the bottomportion of the impactor directly below the entrance of the impactor isan aerosol particle impaction plate that can be used to collect largeaerosol particles such as inorganic acid particles, metal particles, anddust particles. The aerosol particle impaction plate can be made ofmaterials such as stainless steel alloy or polymer. The selection ofmaterials depends on the specific application of the personal sampler.The ratio of the area of the entrance to the area of the aerosolparticle impaction plate can be about 1/10 to 1/1000.

In an embodiment, the size classification can follow human respiratorypatterns (respirable fraction or thoracic fraction) to satisfy OSHAregulations or air quality standards satisfying EPA regulations. In anembodiment the impactor can include 2 or more sub-impactors used toclassify different aerosol particle sizes (e.g., each sub-impactor hasdifferent entrance diameters and exit (to the membrane denuder)diameters). In particular, Example 1 describes an impactor with foursub-impactors to comply with OSHA testing. Additional details aredescribed in Example 1. The diameter (or width) of the impactor can beabout 10 mm to 100 mm. The length of the impactor can be about 5 mm to50 mm.

The membrane denuder operates under the principle of gas diffusion tocollect the gas(es) of interest. When air passes through the membranedenuder (i.e., the air flow travels parallel to the membranes), gasmolecules diffuse to the membrane denuder walls perpendicular to theflow and are absorbed (collected). The remaining aerosol particlescontinue to the filter pack positioned below the membrane denuder. Inthis way, the interference of the gas(es) with the aerosol particles onthe filter pact is substantially reduced (e.g., about 75% or more, about80% or more, about 85% or more, about 90% or more, about 95% or more, orabout 99% or more) or eliminated.

In an embodiment, the membrane denuder can be a porous structure and canbe coated with at least one chemical composition that collects at leastone type of gas (e.g., HCl, SO₂, HF, HNO₃, NH₃, Volatile OrganicCompounds (VOCs) (e.g., aliphatic hydrocarbons, aromatic hydrocarbons,chlorinated solvents, terpenes, and the like), and combination thereof.In an embodiment the (VOCs can include: toluene, benzene, ethylbenzene,acetone, methyl tert-butyl ether, formaldehyde, ethylene glycol,methylene chloride, dichloromethane, trichloroethane, perchloroethylene,n-butyl acetate, 4-phenylchclohexene, limonene, a-pinene, octane,decane, undecane hexane, isodecane, xylene, and combinations thereof).Chemical compositions of the coating materials and the correspondinggas(es) that can be absorbed are listed in Table 1. The amount ofchemical composition can be adjusted depending upon the amount ofexposure expected (if known), the different types of gases to becollected, the time of exposure, and the like. The membrane denuder canbe made out of materials such as fabric (e.g., cellulose filter,glassfiber filter, membrane filter, Teflon membranes, PTFE), paper,film, and the like.

TABLE 1 Coating materials for absorbing gases in the membrane denuderReference Coating Material Gas Absorbed (corresponding to Ex. 1) Oxalicacid NH₃, aniline De Santis and Perrino (1986); Ferm (1979); Cheng(2001) Oleic acid SO₃ Thomas (1955) H₃PO₄ NH₃ Stevens et al. (1978)K₂CO₃ SO₂, H₂S Durham et al. (1978) Na₂CO₃ SO₂, HCl, Forrest et al.(1982) HNO₃, HNO₂ CuSO₄ NH₃ Thomas (1955) Citric Acid NH₃ Langford(1989) PbO₂ SO₂, H₂S Durham et al. (1978) WO₃ NH₃, HNO₃ Branman et al.(1982) MgO HNO₃ Stevens et al. (1978) NaF HNO₃ Slanina et al. (1981)NaCl HNO₃ Perrino et al. (1990) NaOH and guaiacol NO₂ Buttini et al.(1987) Bisulfite- Formaldehyde Cecchini et al. (1985) TriethanolamineGold Gaseous mercury Munthe et al. (1990) Activated carbon Volatileorganic Cooper and Alley (2010) compounds

In an embodiment, the use of a porous membrane provides a much highersurface area than the solid surface provided by conventional denuders,hence yielding a much larger capacity. The membrane denuder includeswalls that are parallel to the gas flow, so that the aerosol particlesare not caught in the membrane denuder. The membrane denuder can have across-section that is selected from an annular pattern, a swirl pattern,grid pattern, plate pattern, a honeycomb pattern, repetitive “V”pattern, a polygonal pattern, an accordion pattern, or a combinationthereof, where the walls are parallel to the gas flow and perpendicularto the filter pack.

In an embodiment, the membrane denuder can have a surface area of about0.01 m² to 100 m² or about 1 m² to 10 m². The diameter of thecross-section can be about 10 mm to 100 mm or about 30 mm to 50 mm. Thelength of the membrane denuder can be about 5 mm to 200 mm or about 10mm to 100 mm. The ratio of the cross-section of the area occupied by themembrane denuder to the cross-section of the area of unoccupied (e.g.,openings in the membrane denuder for particles to fall to the filterpack) is about 0.001 to 0.5.

In an embodiment, the membrane denuder can have a collection capacity ofabout 0.1 g to 2 g for any one or a combination of the gases listed inTable 1. Collection capacity of the denuder depends on the porosity,length and diameter of the denuder, the coating thickness andconcentration of the coating material to the denuder and the diffusioncoefficient of the target gas, and the flowrate through the denuder.

In an embodiment, gas(es) of interest can include volatile organiccompounds (VOCs), chemical warfare agents, and also include thefollowing: aldehydes, aliphatic nitrogen compounds, sulfur compounds,aliphatic oxygenated compounds, halogenated compounds, organophosphatecompounds, phosphonothionate compounds, phosphorothionate compounds,arsenic compounds, chloroethyl compounds, phosgene, cyanic compounds, orcombinations thereof. In one embodiment, the contaminant isacetaldehyde, methyl mercaptan, ammonia, hydrogen sulfide, diethylsulfide, diethyl disulfide, dimethyl sulfide, dimethyl disulfide,trimethylamine, styrene, propionic acid, n-butyric acid, n-valeric acid,iso-valeric acid, pyridine, formaldehyde, 2-chloroethyl ethyl sulfide,carbon monoxide, or combinations thereof.

Embodiments of the present disclosure may include a space between theimpactor bottom surface and the membrane denuder and/or a space betweenthe membrane denuder and the filter pack. The space between each canvary depending upon variables such as dimensions of the variouscomponents, the pumping speed, and the like.

In an embodiment, the filter pack can include one or more filters (e.g.,a first filter and a back up filter (See FIG. 1.3)) disposed on top ofone another. In an embodiment, the filter can include filters forcollecting aerosols of interest such as H₂SO₄ and H₃PO₄ particles. In anembodiment, the aerosol particles that are collected on the filter(s)can have a diameter of about 0.01 μm to 100 μm or about 0.01 μm to 10μm. The filter can be made of a material such as glass fiber, Teflon®,polymer, carbon, ceramic, and a combination thereof. The filter can be afibrous filter, a porous membrane filter, a granular bed filter, or acombination thereof. A fibrous filter includes fibers having a diameteron the order of about 10 nm to 10 μm. In an embodiment, the diameter ofthe fibers is about 20 to 80 nm. A porous membrane filter can be amembrane with pores of about 100 nm to 10 μm. A granular bed filterincludes granules with pores on each granule and between granules ofabout 10 nm to 100 μm. The filter can be about 1 μm to 10 cm thick, andthe length and width can be on the order of cm to meters depending onthe particular application. The type (e.g., material, size, and thelike) of filter can depend, at least in part, upon the intended use ofthe pollutant collection system, the exposure to contaminants, the typeof contaminants, and the like.

In an embodiment, the diameter (or the length or width) of the filter(s)can be about 10 mm to 100 mm or about 30 mm to 50 mm. In an embodiment,the thickness of the filter(s) can be about 0.01 mm to 10 mm or about0.05 mm to 1 mm. Once the air passes through the filter, the air can bedirected out of the collection device.

EXAMPLES

Now having described the embodiments of the present disclosure, ingeneral, the examples describe some additional embodiments of thepresent disclosure. While embodiments of the present disclosure aredescribed in connection with the examples and the corresponding text andfigures, there is no intent to limit embodiments of the presentdisclosure to these descriptions. On the contrary, the intent is tocover all alternatives, modifications, and equivalents included withinthe spirit and scope of embodiments of the present disclosure.

Example 1

In sampling aerosols, the characteristics of particles of differentsizes need to be considered. The hazard caused by inhaled particlesdepends on their chemical composition and on the site at which theydeposit within the respiratory system. Particles which penetrate intothe pulmonary regions of lungs are dominantly deleterious for the humanbody. Impactors are relatively small and can be used to classifyparticles by particle size. In 1977, Marple et al. proposed a parallelimpactor which arranged several impactors with different nozzle sizes inparallel to overcome the sharp penetration characteristics of theimpactor. Arranged on a single-stage impactor, the samplingcharacteristics of the impactor can approximate ACGIH/CEN/ISO-definedrespirable or thoracic sampling convention accurately (Marple, 1977;Trakumas and Salter, 2009).

To remove gases from an aerosol stream and measure their concentrationsseparately, a diffusion denuder system has been widely employed (Ackeret al. 2005; Cheng 2001; Dasch et al. 1989; Hayami 2005; Huang et al,2004; Pathak and Chan 2005; Tsai et al 2004). The original design of thedenuder system was a straight tube (Ferm, 1979; Durham et al, 1986) withinner wall coated with various adsorbents to absorb different gaseousspecies. When air passes through the denuder, gas molecules diffuse tothe wall of the tube and get adsorbed on the wall. A variety of denudershave been developed during recent years, e.g. annular denuder(Possanzini et al. 1983); coiled denuder (Pui et al., 1990); honeycombdenuder (Koutrakis et al, 1993; Sioutas et al., 1996); parallel platedenuder (Eatough et al. 1993) and so on. However, all of these denudershave been designed for sampling in the ambient or indoor environment,where pollutant concentration is very low. In order to be used in anoccupational environment, the denuder system needs more compact designsto increase its capacity in adsorbing gas. In 2001, Tsai et al.developed a personal porous-metal denuder which specifically worked foradsorbing acidic gases and ammonia gas in occupational environment.Field test results showed that the porous-metal denuder has a very highcollection efficiency; however, particle loss in the porous metal discwas also high because particles are forced to penetrate the porous metaldiscs. Therefore, a new device which has both big capacity for gasabsorption and low particle loss rate needs to be developed.

To overcome the limitations discussed above, a new “porous membranedenuder” has been designed. It has both the characteristics of high gascollection efficiency and low particle loss rate. By combining with aparallel impactor and a filter pack to construct a personal sampler tocollect aerosol and hazardous gas simultaneously and respectively, thisnew personal sampler can be used to assess human exposures to a varietyof gaseous and particulate air pollutants in both occupationalenvironment and ambient environment. Below is a description of thedesign of this sampler and its performance evaluation tests to collectsulfur dioxide (SO₂) gas and aerosols.

Description of the Sampler:

As shown in FIG. 2.1, the entire sampling system can include 3 maincomponents in series: a parallel impactor at the front (optional), aporous membrane denuder in the middle and a filter pack at the end.

The parallel impactor at the front is used to classify aerosol sizes andremove larger aerosols to prevent their deposition in the followingdenuder. The design of the parallel impactor is similar to that ofTrakumas et al. (2009). It includes 4 parallel and separated impactors.The different nozzle sizes of each impactor have different cut sizes,that when combined, will create a collection efficiency curve thatfollows a desired pattern, e.g., human respiratory pattern (respirablefraction or thoracic fraction) to satisfy OSHA regulations or airquality stands (PM 2.5, PM 10) satisfying EPA (Environmental ProtectionAgency) regulations (Marple, 1978; Trakumas et al., 2009).

In this design, the size of each impactor has been calculated to followthe American Conference of Governmental Industrial Hygienists (ACGIH)respirable curve with a cut point of 4 μm. The flowrate through eachimpactor is controlled using exit orifices. Because the pressure dropacross the impactor, ΔP, is equal to the dynamic pressure in the nozzlesand the pressure drop across each individual impactor is equal, the exitorifices can be sized using the following equation:

$\begin{matrix}{{Q_{1}^{2}\left( {\frac{1}{S_{1,{in}}^{2}} + \frac{1}{S_{1,{out}}^{2}}} \right)} = {{Q_{2}^{2}\left( {\frac{1}{S_{2,{in}}^{2}} + \frac{1}{S_{2,{out}}^{2}}} \right)} = {\ldots = {Q_{N}^{2}\left( {\frac{1}{S_{N,{in}}^{2}} + \frac{1}{S_{N,{out}}^{2}}} \right)}}}} & \lbrack 2\rbrack\end{matrix}$

where Q is the flowrate through the individual impactor and and S_(N,in)and S_(N,out) are the areas of the inlet nozzles and outlet orifices,respectively.

FIG. 2.2 shows the structure of the impactor, which includes an inletnozzle plate and an impactor plate with exit orifices. Above the exitimpactor there is a collection substrate of the same shape which is madeof cellulose filter to collect particles bigger than the cutsize. Aftersampling, the filter substrate is removed from the sampler and isanalyzed. A gasket between the inlet nozzle plate and the filterimpaction substrate divides the impactor into four compartments. Eachcompartment contains one inlet nozzle, corresponding filter substrateand exit orifice. Parameters of these nozzles are presented in Table 1using a flowrate of 2 L/min.

TABLE 1 Specifications of Impactor nozzle sizes D₅₀ (μm) D_(in) (cm)D_(out) (cm) 6.6 0.236 0.115 4.6 0.186 0.125 3.5 0.156 0.139 2.2 0.1150.236

The porous membrane denuder in the middle is composed of a soft andporous membrane (e.g., fabric, paper, film) coated with a specificchemical to selectively collect target gases by diffusion. The highsurface area resulting from the porosity enables high collectioncapacity in small volume that is important for high concentrationscenarios commonly encountered in industrial settings. The flexibilityof the membrane also allows diverse configurations of the design (e.g.,grid, swirl, as shown in FIG. 2.3) that can maximize available surfacearea and reduce diffusion distance while maintaining low aerodynamicdrag. The denuder wall is parallel to the air flow at all times. Gas isabsorbed on the denuder wall by diffusion. Hence, there is no inherentimpaction of particles on the denuder.

FIG. 2.4 shows the cross structure of the denuder. The denuder is 50 mmin height and 37 mm in diameter and is constructed of cellulose filterpaper, which was selected because of its rigidity and ease in making thecross shape. In addition, cellulose filter is used in NIOSH Method 6004to absorb sulfur dioxide which provides sufficient backgroundinformation for our experiment.

The filter pack of selected filters is to collect the penetrating fineaerosols. There are two filters in the filter pack. The first filtercollects aerosols that pass through the denuder. The second filter,coated with Na₂CO₃, collects acidic gases that evolve from collectedaerosols on the first filter. A filter holder with a diameter of 37 mmis used to support the filters. FIG. 2.5 shows the structure of thefilter pack.

The 3 components, impactor, denuder, and filter pack, are packaged asmodules; thus, it is easy to install and to dissemble. When mixed airflow passes through this personal sampler, larger aerosols will beremoved from the gas stream by the impactor, then target gases will beremoved by the denuder and finally the remaining fine aerosols will becollected on the filter pack.

SO₂ Collection Efficiency and Capacity of the Porous Membrane Denuder

Experiments for measuring gas collection efficiency of the porousmembrane denuder were conducted using SO₂, supplied from a SO₂ cylinderof known concentration at a flowrate of 2 L/min. The porous membranedenuder, two in series, was coated with 15% (w/v) Na₂CO₃/1% glycerin anddried. 9 mM Na₂CO₃ solution was used in the impingers downstream toabsorb gas that penetrated the denuder. Solution in the impinger wasthen analyzed by an ion chromatography (IC) system. By calculating thepenetrating amount of the gas, the collection efficiency of the denuderfor SO₂ gas could be determined accordingly.

FIG. 2.6 shows the collection efficiency of the denuder under differentSO₂ feed concentrations. In the first situation, the concentration ofSO₂ gas was 10 ppm, which is twice the Permissible Exposure Level (PEL)of SO₂ set by OSHA. Two denuders were arranged in series to ensure highcollection efficiency in a relatively long time period. The experimentalresult showed that SO₂ removal efficiency of the fabric denudermaintained above 95% for about four hours. In the second situation, SO₂gas of 1 ppm passed through one denuder. The collection efficiency ofthe denuder remained 100% for 8 hours. Prior research showed that SO2concentration at the phosphate fertilizer plants ranged from 34 ppb to5.6 ppm, while at most sites the concentration was much lower than 1 ppm(Hsu, 2008). Combined with the experimental result stated above, we cansee that two denuders in series in the personal sampler can ensure highSO₂ collection efficiency in eight-hour sampling in most conditions. Ifworkers should stay in place where high SO₂ concentration is possiblefor a long time, e.g., attack tank area and sulfuric acid pump tankarea, the personal sampler can maintain an efficiency higher than 95%for four hours. However, concerning worker health, it is not appropriatefor workers to stay at places with high SO₂ concentration for more thantwo hours.

Aerosol Collection Efficiency and Loss

For measuring particle collection efficiency of the impactor, avibrating orifice aerosol generator (VOAG, Model 3450, TSI Inc.) wasused to generate monodisperse particles of uranine tagged oleic acid.Sampling flowrate of the personal sampler was controlled at 2 L/min tobe consistent with that used for the denuder.

An UV-Aerodynamic Particle Sizer (APS, TSI, Model 3012A) was connectedto the upstream and downstream of the impactor to measure particle'saerodynamic diameter and number/mass concentration at the two sides. Atboth upstream and downstream sampling points, the sampling time was 1minute and it was repeated for 20 times. The geometric standarddeviation for feed aerosol diameter was less than 1.2. And then, themeans of geometric mean diameter and number concentration for each groupof samples were calculated. Finally, penetration percentages of eachparticle size were obtained by dividing the mean number concentrationdownstream the impactor over that upstream the impactor.

${{Penetration}\mspace{14mu} \%} = {\frac{{Mass}\mspace{14mu} {on}\mspace{14mu} {after}\mspace{14mu} {filter}}{{{Mass}\mspace{11mu} {on}\mspace{14mu} {after}\mspace{14mu} {filter}} + {{Mass}\mspace{14mu} {on}\mspace{14mu} {filter}\mspace{14mu} {impaction}{\mspace{14mu} \;}{substrate}}} \times 100\%}$

FIG. 2.7 shows the penetration characteristics of the impactor. Thesolid and dashed curves represent the respirable convention and thetheoretical characteristic of the impactor, respectively. Triangle andsquare points in FIG. 2.7 are two groups of experimental data. We cansee from FIG. 2.7 that the overall tendency of the experimental data wasin excellent accordance with the respirable curve.

To test particle loss in the denuder, the VOAG was also used to producemonodisperse particles of various sizes. The sampling tubes of theUV-APS were located at upstream and downstream of the denuder. Samplingperiod was 1 minute with 20 replications, as in aerosol collection test.The mean number concentration before and after the denuder were close toone other, as shown in FIG. 2.8. Number concentration for differentparticle sizes was slightly different due to different dilution air flowrates and frequencies used in the test. Particle loss was under 5% forparticle size from 1 to 10 μm. Particle loss percent of each aerodynamicdiameter is also shown in FIG. 2.8.

CONCLUSION

A novel personal sampler, which includes a parallel impactor, a porousmembrane denuder and a filter pack, has been designed, built and tested.The porous membrane denuder was proven to maintain a collectionefficiency of SO₂ gas higher than 95% for four hours with a feedconcentration of 10 ppm and 100% for eight hours with a feedconcentration of 1 ppm, which showed that the capacity of the denuder islarge enough for measurement in both occupational and ambientenvironments. The experiments also show that aerosol penetrationcharacteristic of the parallel impactor follows the ACGIH respirablecurve excellently and particle loss in the denuder for particles of 1 to10 μm are under 5%.

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Example 2 Experimental System and Procedures Material

To compare the porous membrane denuder's (PMD) capacities withcommercially available denuder, experiments were carried out with PMDIII, PMD IV (i.e., 3^(rd) and 4^(th) generation) and a glass honeycombdenuder (GHD). The GHD has been commercialized and integrated in adenuder-filter system, which is called “ChembComb Speciation SamplingCartridge” (Model 3500, Thermo Electron Co., Inc.). The GHD is 47 mm indiameter and 38 mm long. Its internal surface area of 508 cm² is madepossible by 212 hexagonal flow channels that are 2 mm on each side. TheGHD has a weight of 106 g. The schematic of PMD III is shown in FIG.3.1. PMD IV has the same structure as PMD III, only with more zigzaginserts. Properties of the PMDs and GHD are listed in Table 1. Both thePMDs and GHD were coated with 10% sodium carbonate (Na₂CO₃)/glycerin toabsorb SO₂ and other acidic gases.

TABLE 1 Properties of PMD III, PMD IV and GHD Diameter Length Number ofChannel opening Weight Denuder (mm) (mm) Channels area (mm²) (g) PMD III47 50 192 8.58 6~9 PMD IV 50 280 5.90 GHD 38 212 6.88 106

Sampling and Analysis Denuder Collection Efficiency

The experimental system for capacity test is shown in FIG. 3.2. Intesting PMDs' performance in occupational environment, the feed SO₂concentration used was 10 ppm, which is twice the Permissible ExposureLevel (PEL) of SO₂ set by U.S. Occupational Safety and HealthAdministration (OSHA). The flow rate of the gas stream, 2 L/min, wascontrolled by a mass flow controller (MFC; OMEGA, Model FMA 5520). AnSO₂ monitor (International Sensor Technology, Inc., Model IQ-350) whichcan monitor the SO₂ concentration in real time was connected to theupstream and downstream of the sampler to measure SO₂ gasconcentrations. Two impingers in series were connected downstream of thesampler using 9 mM Na₂CO₃ solution to absorb gas that penetrated thedenuder. Solution in the two impingers was changed every 30 minutes.Most of the exhaust gas was collected by the first impinger, while thesecond impinger was used to check whether the first one broke through.After sampling, hydrogen peroxide (H₂O₂) was added to the samplesolution to oxidize sulfite to form sulfate. Time weighted average (TWA)concentration of sulfate ions was determined by an IC system (ModelICS-1500, DIONEX Inc.).

For real-time gas monitoring using the SO₂ monitor, the collectionefficiency (Eff) of SO₂ can be obtained by measuring the feedconcentration (C_(u)) upstream and the exit concentration (C_(d))downstream of the personal sampler. Eff at any given time can becalculated by the following equation:

$\begin{matrix}{{Eff} = {\frac{c_{u} - c_{d}}{c_{u}} = {1 - \frac{c_{d}}{c_{u}}}}} & (1)\end{matrix}$

When the impinger method was used for measuring downstream gasconcentration, the exit gas concentration in Equation (1) was thesummation of the concentrations in impingers 1 and 2.

In addition to testing SO₂, the system has also been tested for 10 ppmHCl and 4 ppm HNO₃ using PMD III and PMD IV. Both concentrationscorrespond to twice their OSHA standards.

Results and Discussion

The collection efficiencies of the two different types of PMDs and theGHD are shown in FIG. 3.3. It can be seen that as the number of channelsincreases and channel cross-sectional area decreases, the capacity ofthe denuder increases. 5-hour TWA collection efficiencies of PMD III,and IV were 90.9% and 97.2%, respectively, while that of the GHD was96.6%. Compared with the GHD, PMD IV has slightly higher collectionefficiency. However, the weight of the GHD is about 10 times greaterthan that of the PMD IV. In addition, since the PMDs are made of filterpaper, they are relatively cheap. Furthermore, they are disposable andtherefore users do not have to be concerned if the unit containsresidual from the previous test. These advantages make the PMDs superiorto traditional denuders made of glass or metals for applications wherelight weight, low cost and ease of operation are important features.

The results for testing HCl and HNO₃ are displayed in FIG. 3.4. Asshown, PMD III and IV are more efficient for collecting HNO₃ than HCldue to lower HNO₃ feed concentration. PMD IV, which has more channels,has excellent performance for both gases in the entire 4 hours.

Testing of PMD V

PMD V was specially designed to have a more flexible structure.Cellulose membrane (Whatman Grade 40) was cut by a laser plotter into anaccordian shape cross-section. When folded, the edges of the PMD fittedthe cylindrical denuder system very well, as shown in FIG. 3.5. Thedevelopment of PMD V shows the flexibility of porous membrane inconstructing denuders of various shapes. In addition, compared tomulti-grid construction of PMD III and IV, PMD V is much easier tofabricate and assemble. It is also easier to adopt PMD V to smaller orlonger sampling system.

PMD V developed in this test was 70 mm long and 20 mm in diameter (whenfolded). It was coated with 10% (w/v) Na₂CO₃/glycerin solution and driedbefore experiments. PMD V's capacity for SO₂ gas of 10 ppm was tested.Experimental system is shown in FIG. 3.2. Sampling flow rate was kept at2 L/min. In all three experiments, PMD V exhibited a collectionefficiency of 100% for 8 hours, as shown in FIG. 3.6. It is clear thatPMD V has capacity high enough for applications to occupationalsampling.

REFERENCES, WHICH ARE INCORPORATED HEREIN BY REFERENCE

-   Koutrakis P., Wolfson J. M., Slater J. L., Brauer M., Spengler J.    D., Stevens R. K. and Stones C. L. (1988) Evaluation of an annular    denuder/filter pack system to collect acidic aerosols and gases.    Enuir. Sci. Technol. 22, 1463-1468.-   lanniello, A., Beine, H. J., Landis, M. S., Stevens, R. K.,    Esposito, G., Amoroso, A. and Allegrini, I. (2007). Comparing field    performances of denuder techniques in the high Arctic. Atmospheric    Environment, 41(8), 1604-1605-   Trakumas, S. and. Salter, E. (2009) Parallel particle impactor—novel    size-selective particle sampler for accurate fractioning of    inhalable particles. Journal of Physics: Conference Series, 151,    012060.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso include individual concentrations (e.g., 1%, 2%, 3%, and 4%) andthe sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within theindicated range. In an embodiment, the term “about” can includetraditional rounding according to significant figures of the numericalvalue. In addition, the phrase “about ‘x’ to ‘y’” includes “about toabout ‘y’”.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations, andare set forth only for a clear understanding of the principles of thedisclosure. Many variations and modifications may be made to theabove-described embodiments of the disclosure without departingsubstantially from the spirit and principles of the disclosure. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure.

We claim:
 1. A collection device, comprising: a membrane denuder,wherein the membrane denuder is a porous structure that includes atleast one chemical composition that collects at least one type of gas;and a filter pack, wherein the filter pack collects aerosol particlesthat pass through the membrane denuder, wherein the membrane denuder isdisposed on top of the filter pack so that the air flow of the gas intothe device passes through the membrane denuder before contacting thefilter pack.
 2. The collection device of claim 1, further comprising: animpactor disposed on the membrane denuder on the side opposite thefilter pack so that the gas passes through the impactor beforecontacting the membrane denuder, and wherein the impactor removes largeaerosol particles.
 3. The collection device of claim 2, wherein theimpactor includes two or more inlet orifices and exit orifice, whereindimensions of the inlet orifices are different, and wherein the inletorifices are used to classify different sizes of aerosol particles 4.The collection device of claim 1, wherein the membrane denuder includesporous walls that are parallel to the air flow and perpendicular to thefilter pack.
 5. The collection device of claim 1, wherein the chemicalcomposition has an affinity for one or more of the following: HC1 gas,SO₂ gas, HF gas, HNO₃ gas, NH₃ gas and volatile organic compounds. 6.The collection device of claim 1, wherein the filter pack filters outaerosols such as H₂SO₄ and H₃PO₄.
 7. The collection device of claim 1,wherein the chemical composition has an affinity for one or more of thefollowing: HC1 gas, SO₂ gas, HF gas, HNO₃ gas, NH₃ gas, and volatileorganic compounds, and wherein the filter pack filters out aerosols suchas H₂SO₄ and H₃PO₄, wherein collection of the gas and aerosolssimultaneously does not result in interference between the gas andaerosol.
 8. The collection device of claim 1, wherein the membranedenuder has a cross-section that is selected from a swirl pattern, gridpattern, plate pattern, polygonal pattern, multi-annular pattern, ahoneycomb pattern, a repetitive “V” pattern, an accordion pattern, and acombination thereof.
 9. A method of collecting aerosol particles andcollecting gas, comprising: removing large particles from a gas flowusing an impactor; collecting one or more gas types using a membranedenuder after removing the large particles; and collecting one or moreaerosol types using a filer pack after collecting the gas using thedenuder.
 10. The method of claim 9, wherein the chemical composition hasan affinity for one or more of the following: HCl gas, SO₂ gas, HF gas,HNO₃ gas, NH₃ gas, and volatile organic compounds.
 11. The method ofclaim 9, wherein the filter pack collects aerosols such as H₂SO₄ andH₃PO₄.
 12. The method of claim 9, wherein the chemical composition hasan affinity for one or more of the following: HCl gas, SO₂ gas, HF gas,HNO₃ gas, NH₃ gas, and volatile organic compounds, and wherein thefilter pack collects aerosols such as H₂SO₄ and H₃PO₄, whereincollection of the gas and aerosols simultaneously does not result ininterference between the gas and aerosol.
 13. The method of claim 9,wherein the membrane denuder has a high surface area and open porousstructure that allows more efficient absorption and higher capacity ofgas molecular than solid surface denuders.
 14. The method of claim 9,wherein the membrane denuder does not require regeneration.
 15. Themethod of claim 9, wherein the membrane denuder has a cross-section thatis selected from a swirl pattern, grid pattern, plate pattern, polygonalpattern, multi-annular pattern, a honeycomb pattern, a repetitive “V”pattern, an accordion pattern, and a combination thereof.